1. Technical Field
The present invention relates to an illumination unit and an endoscopic apparatus provided with the same.
2. Description of Related Art
Endoscopic apparatus for observing tissues in a body cavity has been known broadly. Generally, an endoscopic apparatus has a configuration in which white light emitted from a white light source such as a xenon lamp is supplied as illumination light to a to-be-observed region in a body cavity through a light guide and an image based on reflected light from the to-be-observed region irradiated with the white light is captured by an imaging device to generate an observation image. In recent years, an endoscopic apparatus having observation modes using special light is also being used. The observation modes are narrow-band light observation for observing blood capillaries or microscopic structures in a tissue surface layer while biological tissues are irradiated with narrow-band light with a specific wavelength, fluorescent observation using intrinsic fluorescence or drug fluorescence, etc. As a light source of an endoscopic apparatus for irradiation with special light, there has been known a configuration in which light emitted from a white light source such as a xenon lamp is made to pass through a rotary filter having a predetermined light absorption property to selectively extract light in a desired wavelength band so that a subject is irradiated with the extracted light (see JP-A-2006-218283). In the endoscopic apparatus having the aforementioned configuration, B light with a narrow-band wavelength and G light with a narrow-band wavelength, as special light for narrow-band light observation, can be emitted at a predetermined outgoing light quantity ratio. The intensity of the special light in this case is adjusted by an aperture unit provided on the way of an optical path from the white light source. The outgoing light ratio between the B light and the G light is set by light transmittances of a B filter and a G filter in the rotary filter.